Fluid pressure motor



Oct. 26, 1965 R. J. KNABLE FLUID PRESSURE MOTOR 2 Sheets-Sheet 1 FiledSept. 20, 1963 m m E V m RAYMOND J. KNQBLE Oct. 26, 1965 R. J. KNABLE3,213,765

FLUID PRESSURE MOTOR Filed Sept. 20, 1963 2 Sheets-Sheet 2 4 Hum, Mg IATTORNEYS United States Patent 3,213,765 FLUHD PRESSURE MOTOR Raymond E.Knable, Bellwood, 111., assignor to Parker- Hannifin Corporation,Cieveiand, Ohio, a corporation of Ohio Filed Sept. 20, 1963, Ser. No.310,238 28 Claims. (Ci. 92-52) The invention relates generally to fluidpressure actuators and seeks to provide a novel cylinder and pistonarrangement wherein a piston operated actuator movement is initiated bya large force application and is then sustained or continued by asmaller force application.

An object of the invention is to provide a cylinder, piston and actuatorarrangement of the character stated wherein a double acting cylinder andpiston means is included to bring about movement of the actuator in'bothdirections, such movement in each direction being initiated by a largeforce application and continued or sustained by a smaller forceapplication.

It is another object of the invention to provide a pair of largediameter cylinders and a small diameter cylinder in which the heads ofthe latter are also large pistons of the large cylinders, the smallcylinder having a small piston with a rod attached thereto, the smallpiston being movable by contact with either of the large pistons formovement thereby during the first part of a stroke of the small piston,and with the small piston being movable by fluid pressure away from thecontacting large piston during the remaining part of the small pistonstroke.

It is another object of the invention to provide a small cylinder with asmall piston therein movable by fluid pressure and with a pair of largecylinders with large pistons therein, and with means whereby fluidpressure acting on each large piston assists in moving the small pistonfor a part of its stroke in either direction.

Another object of the invention is to provide a novel fluid pressureactuator of the character stated wherein there are provided a tandemcylinder-piston arrangement including a large cylinder with a head ateach end thereof and a smaller cylinder with an inner end telescoped inthe larger cylinder through one head thereof and a large piston securedon the telescoped end of the smaller cylinder for movement in unisontherewith and slidable in the large cylinder between the heads thereon,the smaller cylinder also having a head on its outer end, a small pistonslidable in the small cylinder between the head on the small cylinderand an abutment portion of the large piston and to which an actuator rodis attached to project through the other large cylinder head, and meansthrough which pressure fluid may be directed into and from the cylindersto bring about reciprocation of the pistons individually and in unison.

A further object of the invention is to provide a fluid pressureactuator of the character stated wherein an initial portion ofretraction of the actuator rod is eflected by pressure fluid actionagainst the large piston followed by continued retraction efl'ectedsolely by pressure fluid action against the small piston.

Yet another object of the invention is to provide a fluid pressureactuator of the character stated wherein an initial portion ofretraction of the actuator rod is effected by pressure fluid actionagainst the large piston and attendant movement of the large piston andthe small cylinder followed by continued projection elfected by pressurefluid action against the small piston and movement thereof independentlyof movement of the small cylinder.

Still another object of the invention is to provide a fluid pressureactuator of the character stated wherein the large piston is arranged tobottom in each stroke direction in the large cylinder and includesthereon means for limit- "ice ing movement of the small piston in thedirection of projection of the actuator rod thereby to limit the amountof movement in unison of the pistons in each direction, and here beingincluded stop means on the small cylinder to limit movement ofprojection of the actuator rod and cause initial movement of retractionof said rod in unison with the small cylinder.

A further object of the invention is to provide a fluid pressureactuator of the character stated wherein the large piston bottomsdirectly against one or the other of the large cylinder heads at the endof each reciprocation stroke of the small cylinder, and the small pistonbottoms directly against the small cylinder head to limit the retractionstroke of the actuator rod.

A still further object of the invention is to provdie a fluid pressureactuator of the character stated wherein the means through whichpressure fluid may be directed into and from the cylinders comprises aninlet and exhaust passage formed in each cylinder head and communicatingwith an end of the cylinder on which the particular head is mounted.

With the above and other objects in view that will hereinafter appear,the nature of the invention will be more clearly understood by referenceto the following detailed description, the appended claims and theseveral views illustrated in the accompanying drawing:

In the drawing:

FIGURE 1 is a partial longitudinal section and side elevationillustrating the invention, the actuator rod being shown in itsprojected position.

FIGURE 2 is a vertical cross section taken on the line 22 on FIGURE 1.

FIGURE 3 is a side elevation, parts being broken away and the actuatorrod being shown in a partially retracted position.

FIGURE 4 is a partial longitudinal section and side elevation of asecond form of the invention.

In the example of embodiment of the invention disclosed in FIGURES 1 to3 herein, the novel fluid pressure actuator includes a large cylinder 5having heads 6 and 7 secured on the ends thereof and in assembly betweenhead plates 8 and 9 by securing bolt means 10, suitable sealing means 11being provided at each cylinder end and head juncture.

A sealing bearing ring 12 is threadably mounted at 13 in the plate 8 andhas an extension 14 projecting into the center bore 15 of the largecylinder head 6. A similar seal bearing ring 16 is threadably mounted at17 in the plate 9 and has an extension 18 projecting into the centerbore 19 of the large cylinder head 7. In addition to the sealing means20 provided in each seal bearing ring 12 and 16 a sealing means 21surrounds each ring extension 14 and 18 within the respective cylinderhead 6 or 7.

A large piston 22 is reciprocable within the large cylinder 5 betweenthe heads 6 and 7, and said piston has a bore 23 therein, together witha threaded counterbore 24 into which one end of a small cylinder 25 isthreadably attached in the manner clearly illustrated in FIGURE 1. Theattached small cylinder end is surrounded by a seal 26 within thethreaded counterbore 24.

At its outer end the small cylinder 25 has an anchor ring 27 securedthereon by conventional slot and ring means 28, and a head 29 is securedto the small cylinder end and to the ring 27 by bolt means 30, asuitable seal being provided at the head and cylinder juncture as at 31.

It will be observed that the small cylinder 25 is slidable through theseal bearing ring 16 and its extension 18, and a small piston 32 isreciprocable in the cylinder and has an actuator rod 33 secured theretoas at 34. The rod 33 extends through the large piston 22, the largecylinder head 6 and the plate 8, being slidable through the seal bearingring 12 and its extension 14 as clearly shown in FIGURE 1. The rod 33has provision at for attachment with any device to be moved or actuatedby reciprocation of the rod.

The large piston bore 23 and the counterbore 24 result in the provisionof an abutment shoulder 36 on the large piston 22, said shoulderprojecting inwardly with respect to the inner diameter of the smallcylinder 25 so as to be engageable by the small piston 32, as shown inFIGURE 1. It will be apparent by reference to FIGURE 1 that when thelarge piston 22 is bottomed against the large cylinder head 6 and thesmall piston 32 is bottomed or stopped against the large piston shoulder36 a limit will be provided for the outward projection of the actuatorrod 33. It will also be apparent that when the large piston 22 isbottomed against the large cylinder head 7 as shown in FIGURE 3 and thesmall piston 32 is stopped against the small cylinder head 29 a limitwill be placed upon the in stroke or retraction of the actuator rod 33.

While various installations of the fluid pressure actuator may be made,an example is disclosed schematically herein. In this schematic showing,in FIGURE 1, there is included a fluidpressure circulating pump 40connected by a receiving line 41 with a supply reservoir 42 and by adelivery line 43 with a four-way control valve 44 which is alsoconnected by a return line 45 with the supply reservoir 42. The valve 44also is connected by a flow and return line 46 with the port 37 of thelarge cylinder head 6, and by a flow and return line 47 with the port 38of the large cylinder head 7. The small cylinder port 39 also has a flowand return line 48 connected therewith and through the T-connection 49and the previously mentioned flow and return line. 47 with the valve 44.Since head 29 to which line 48 is connected is movable relative tocylinder 5, line 48 should be in the form of a flexible hose orotherwise adapted to permit such movement.

When the actuator rod 33 is in its projected position as illustrated inFIGURE 1, and it is desired to retract the rod, the valve 44 will beconditioned as illustrated in FIG URE 1 to direct pressure fluid throughthe large cylinder port 37 into the interior of the large cylinder andagainst the left hand ends of the large piston 22 and the small piston32. This applied fluid pressure will serve to move the large piston 22and the attached small cylinder 25 toward the right as viewed in FIGURE1, and with them the small piston 32 and the connected actuator rod 33,

the large piston abutment or stop shoulder 36 being in contact with thesmall piston 32 as long as the external load on rod 33 exceeds the fluidpressure force being applied to the left side of small piston 32. Whenthe external load exceeds this force, piston 32 will move away fromshoulder 36 and continue to move until it contacts head 29. Meanwhile,piston 22 bottoms against head 7 to limit its stroke. At this time fluidis expelled from behind the large piston 22 out through the head port 38and line 47, the valve 44 and the return line 45 to the reservoir 43 andfluid will be expelled from the right side of piston 32 through thesmall cylinder head port 39, the

lines 48 and 47, the valve 44 and the return line 45 to the reservoir42. It will be apparent that in the retraction of the actuator rod 33the movement initially is imparted by force applied to the large piston22 and later the movement of retraction of the piston 32 and the rod 33will be sustained or continued by the smaller force applied to the smallpiston 32.

As in the case of the retraction of the actuator rod, projection of therod also is initiated by a large force applied to the large piston 22,and then is continued or sustained by a smaller force applied to thesmall piston 32. It is to be understood that when the rod is to beprojected the small piston 32 may be at the limit of its in stroke, inthe present illustration, bottomed against the small cylinder head 29.This time pressure fluid will be directed from the reservoir 42, throughthe line 41, pump 40, line 43, the now reversed valve 44 and the lines47 and 48 into the large cylinder 5 through the head port 38 and intothe small cylinder 25 through the head port 39. The pressure fluid thusintroduced will, of course, be initially active against the large piston22 and will cause said piston and the attached small cylinder 25 to moveto the left from the FIGURE 3 position. The small piston 32 having beenstopped against or bottomed on the small cylinder head 29 will, ofcourse, move with the small cylinder 25 and the large piston 22 to whichit is attached. After the external load on rod 33 becomes less than thefluid pressure force acting directly on piston 32, piston 32 moves awayfrom head 29 and continues its stroke while piston 22 bottoms againsthead 6 and with piston 32 ultirnately bottoming against shoulder 36.

In the FIGURE 4 form of the invention there is a second large cylinder53 for assisting movement of small piston 32 during part of its strokein either direction. Second large cylinder 53 is attached to a firstlarge cylinder 5, the latter being identical with cylinder 5 of FIGURE 1and therefore described with like reference numerals. Small cylinder 25in FIGURE 4 is likewise identical with small cylinder 25 of FIGURE 1,except that head 29 of FIGURE 1 is replaced by a head 29 which is formedto serve as a piston for cylinder 53. Cylinder 53 is identical tocylinder 5 except that head 6 does not have its opening 15 extendingcompletely therethrough, nor is there a head plate 8 attached thereto.Reference numerals for parts of cylinder 53 are the same as the numeralsof the corresponding parts of cylinder 5 except with the primedesignation, and therefore further description of cylinder 53 isunnecessary.

The ends of a cylindrical tube 55 have a close guiding fit over theunthreaded ends of glands 18, 18 and butts against head plates 9, 9 tolocate the two cylinders 5, 53 in a fixed axially spaced relationship. Avent opening 56 is provided in tube 55 for draining off any hydrau licfluid which may leak into tube 55 past packing glands 18, 18 Heads 6, 7,9 and 6 are held in position on their respective cylinders and withreference to tube 55 by suitable tie rod bolts 10 which extend from oneend to the other of the assembly and pass through the heads at theirfour corners, the heads being square in end view outline.

The piping from four-way valve 44 to cylinder 5 is the same as in FIGURE1 but branch line 48 from line 47 connects to port 37 of head 6 andbranch line 57 from line 46 is added to connect with port 38 In theoperation of the FIGURE 4 form, and with the parts in the positionillustrated, fluid under pressure from pump 40 will pass through lines46, 57 and ports 37, 38 to the left side of large pistons 22, 29 andthrough bore 23 to the left side of small piston 32. As long as theexternal load on rod 33 is greater than the fluid pressure force exertedon the left side of small piston 32, the latter will remain in contactwith shoulder 36 on piston 22 and be moved by the latter in right handdirection for retracting rod 33. It will be noted that at this timefluid pressure acting on the left side of piston 29 is transmitted topiston 22 through cylinder tube 25 so that piston 32 is moved by theforce acting on both of the large pistons 22, 29

As soon as the external load on rod 33 becomes less than the fluidpressure force being applied to the left side of small piston 32, thelatter will move away from shoulder 36 and will continue to move untilit bottoms on shoulder 36 of piston 29 Meanwhile, piston 22 will havereached the end of its stroke by bottoming on head 7 and piston 29 willlikewise be at the end of its stroke adjacent head 6 During theretraction stroke of rod 33, fluid will be expelled from the right handsides of pistons 22, 29 and 32 through line 47 to reservoir 42, thefluid from the right hand side of piston 32 first passing throughopening 23 in piston 29 To extend rod 33 of FIGURE 4, valve 44 is turnedto connect pump 40 to line 47 and reservoir 42 with lines 46, 57. Fluidunder pressure is then admitted to ports 38, 37 to move pistons 22, 29to the left and through port 23 to act against the right hand side ofpiston 32. As long as the load on rod 33 exceeds the force applied tothe right hand side of piston 32 by fluid pressure, the latter remainsin contact with shoulder 36 and is moved by the combined effect of fluidpressure acting on pistons 22, 29 When the load on rod 33 becomes lessthan the fluid pressure force applied to the right hand side of piston32, the latter moves away from shoulder 36 to complete :its stroke.

While two examples embodying the invention are disclosed herein,together with schematic examples of installation, it is to be understoodthat other variations may be made without departing from the spirit andscope of the invention as defined in the appended claims.

I claim:

1. In a fluid pressure actuator the combination of a large cylinderhaving a head at each end thereof, a small cylinder having an inner endtelescoped in the large cylinder through one head thereof, a largepiston secured on the telescoped end of the small cylinder for movementin unison therewith and slidable in the large cylinder between the headsthereon, said small cylinder also having a head on its outer end, asmall piston slidable in the small cylinder, between the head on thesmall cylinder and an abutment movable with the large piston, anactuator rod attached to and moveable with the small piston andprojecting through the other head on the large cylinder, and meansthrough which pressure fluid may be directed into and from the cylindersto bring about reciprocation of the pistons individually and in unisonin said cylinders.

2. Fluid pressure actuator structure as defined in claim 1 wherein thelarge piston is provided with a center bore through which the actuatorrod extends from the small piston and through which pressure fluid isdirected against and from the small piston.

3. Fluid pressure actuator structure as defined in claim 1 wherein thelarge piston is provided with a center bore through which the actuatorrod extends from the small piston and through which pressure fluid isdirected against and from the small piston, said large piston alsohaving a counterbore in which the inner end of the small cylinder issecured and which provides for a radial inward extension of the largepiston constituting an abutment engageable by the small piston wherebysaid pistons move in unison.

4. In a fluid pressure actuator the combination of a large cylinderhaving a head at each end thereof, a small cylinder having an inner endtelescoped in the large cylinder through one head thereof, a largepiston secured on the telescoped end of the small cylinder for movementin unison therewith and slidable in the large cylinder between the headsthereon, a small piston slidable in the small cylinder, an actuator rodattached to and movable with the small piston and projecting through theother head on the large cylinder, and means through which pressure fluidmay be directed into and from the cylinders simultaneously to bringabout reciprocation of the pistons individually and in unison in saidcylinders in at least one direction of movement of the actuator rod.

5. In a fluid pressure actuator the combination of a large cylinderhaving a head at each end thereof, a small cylinder having an inner endtelescoped in the large cylinder through one head thereof, a largepiston secured on the telescoped end of the small cylinder for movementin unison therewith and slidable in the large cylinder between the headsthereon, said small cylinder also having a head on its outer end, asmall piston slidable in the small cylinder between the head on thesmall cylinder and an abutment movable with the large piston, anactuator rod attached to and movable with the small piston andprojecting through the other head on the large cylinder, and meansthrough which pressure fluid may be directed into and from the cylindersto bring about reciprocation of the pistons individually and in unisonin said cylinders in each direction of movement of the actuator rod.

6. Fluid pressure actuator structure as defined in claim 5 wherein stopmeans is provided on the small cylinder for limiting movement of thesmall piston away from the abutment and stop means is provided on thelarge cylinder for limiting movement of the large piston in eachdirection, said stop means and the means through which pressure fluidmay be directed into and from the cylinders being so cooperativelyarranged that in the efiecting of each actuator rod stroke movement themovement will initially be caused by pressure fluid force applicationagainst the large piston to move the same and the small cylinder andsmall piston in unison and then be continued by pressure fluid forceapplication to the small piston to move the same and the actuator rodindependent of the movement of the large piston and the small cylindersecured thereto.

7. Fluid pressure actuator structure as defined in claim 6 wherein thelarge piston is provided with a center bore through which the actuatorrod extends from the small piston and through which pressure fluid isdirected against and from the small piston, said large piston alsohaving a counterbore in which the inner end of the small cylinder issecured and which provides for a radial inward extension of the largepiston constituting the small piston engageable abutment movable withthe large piston.

8. Fluid pressure actuator structure as defined in claim 5 wherein themeans through which pressure fluid may be directed into and from thecylinders includes a port opening through one large cylinder head intoone end of the large cylinder to direct pressure fluid against and awayfrom one end of the large piston and one end of the small piston, a portopening through the other large cylinder head into the other end of thelarge cylinder to direct pressure fluid about the small cylinder andagainst and away from the other end of the large piston, and a portopening through the small cylinder head to direct pressure fluid intoand from the small cylinder at the other end of the small piston.

9. Fluid pressure actuator structure as defined in claim 5 wherein themeans through which pressure fluid may be directed into and from thecylinders includes a port opening through one large cylinder head intoone end of the large cylinder to direct pressure fluid against and awayfrom one end of the large piston and one end of the small piston, a portopening through the other large cylinder head into the other end of thelarge cylinder to direct pressure fluid about the small cylinder andagainst and away from the other end of the large piston, and a portopening through the small cylinder head to direct pressure fluid intoand from the small cylinder at the other end of the small piston, thelarge piston being provided with a center bore through which theactuator rod extends from the small piston and through which pressurefluid is directed against the small piston, said large piston alsohaving a counterbore in which the inner end of the small cylinder issecured and which provides for a radial inward extension of the largepiston constituting the small piston engageable abutment movable withthe large piston.

10. Fluid pressure actuator structure as defined in claim 5 wherein themeans through which pressure fluid may be directed into and from thecylinders includes a port opening through one large cylinder head intoone end of the large cylinder to direct pressure fluid against and awayfrom one end of the large piston and one end of the small piston, a portopening through the other large cylinder head into the other end of thelarge cylinder to direct pressure fluid about the small cylinder andagainst and away from the other end of the large piston, and a portopening through the small cylinder head to direct pressure fluid intoand from the small cylinder at the other end of the small piston, thelarge piston being provided with a center bore through which theactuator rod extends from the small piston and cooperating with a centerbore in said one large cylinder head and its port in directing pressurefluid into and from said one end of the large cylinder, said largepiston also having a counterbore in which the inner end of the smallcylinder is secured and which provides for a radial inward extension ofthe large piston constituting the small piston engageable abutmentmovable with the large piston, the other large cylinder head including acenter bore cooperating with its port in directing pressure fluid intoand from the other end of the large cylinder, and there also beingincluded a slide guide means for each of the actuator rod and the smallcylinder and each including a projection into the center bore of one ofthe large cylinder heads.

11. Fluid pressure actuator structure as defined in claim 6 wherein thestop means for limiting movement of the large piston constitutes adirect bottoming of the large piston against the heads on the largecylinder.

12. Fluid pressure actuator structure as defined in claim 6 wherein thestop means for limiting movement of the large piston constitues a directbottoming of the large piston against the heads on the large cylinder,and the stop means on the small cylinder constitutes a direct bottomingof the small piston against the small cylinder head.

13. In a fluid pressure actuator, the combination of a first largecylinder and a second large cylinder each having ahead at each endthereof, a small cylinder having one of its ends telescoped into thefirst large cylinder through one head thereof and havings its other endtelescoped into the second large cylinder through one head thereof, saidsmall cylinder having a first head and a second head secured thereto ateach of its opposite ends, said first head being within the first largecylinder and serving as a first large piston and said second head beingwithin the second large cylinder and serving as a second large piston, asmall piston slidable in the small cylinder between said first andsecond heads, an actuator rod attached to and movable with the smallpiston and projecting through the other head on said first largecylinder, and means through which pressure fluid may be directed intoand from the cylinders to bring about reciprocation of the pistons.

14. The actuator of claim 13 in which the large cylinders are rigidlyconnected to prevent relative movement therebetween.

15. The actuator of claim 13 in which each of the large pistons has anabutment engageable by the small piston whereby movement of the largepistons imparts movement to the small piston.

.16. The actuator of claim 13 in which each of the large pistons has anabutment engageable by the small piston whereby movement of the largepistons imparts movement to the small piston, said abutments beingspaced to permit movement of the small piston therebetween.-

17. The actuator of claim 13 in which each of the large pistons has anopening therethrough to communicate the interior of each large cylinderwith the interior of the small cylinder for directing fluid to and fromthe small cylinder.

18. The actuator of claim 13 in which each large cylinder is divided infirst and second chambers by the respective large piston, and means forcommunicating said first chambers with the interior of the smallcylinder for directing fluid to and from the small cylinder.

19. The actuator of claim 18 in which said second chambers are sealedfrom the interior of the small cylinder.

20. The actuator of claim 13 in which the large cylinders are'rigidlyconnected to means of a tube extending therebetween-and said tube has anopening therein for venting any leakage fluid entering said tube fromsaid large cylinders.

21. In a fluid pressure actuator the combination of a small diametercylinder having a small piston therein and first and second largediameter cylinders having respective first and second large connectedpistons therein, said large pistons each being separately engageablewith said small piston for moving the same, and means for simultaneouslydirecting fluid to said large cylinders for simultaneously applyingforce to both said largepistons to impart movement to said small pistonregardless of which large piston is in contact therewith.

22. The actuator of claim 21 in which said small piston has a strokelonger than the stroke of the large pistons and is movable by fluidpressure independently of movement of the large pistons.

23. The actuator of claim 21 in which the large pistons comprise theheads of the small cylinder.

24. In a fluid pressure actuator the combination of a small diametercylinder having a small piston therein and first and second largediameter cylinders having respective first and second large connectingpistons therein, said large pistons each being separately engageablewith said small piston for moving the same, and means for directingfluid to said large cylinders for simultaneously applying force to bothsaid large pistons to impart movement to said small piston regardless ofwhich large piston is in contact therewith, said small piston having astroke longer than the stroke of the large pistons and being movable byfluid pressure independently of movement of the large pistons.

25. In a fluid pressure actuator the combination of a small diametercylinder having a small piston therein and first and second largediameter cylinders having respective first and second large connectedpistons therein, said large pistons each being separately engageablewith said small piston for moving the same, and means for directingfluid to said large cylinders for simultaneously applying force to bothsaid large pistons to impart movement to said small piston regardless ofwhich large piston is in contact therewith, the large pistons comprisingheads of the small cylinder.

26. In a fluid pressure actuator, the combination of first and secondlarge diameter cylinders each having a head at each end thereof and eachhaving therein a respective first large piston and a second largepiston, said large pistons being operatively connected to one another, asmall diameter cylinder having therein a small piston and having each ofits opposite ends telescoped into one of said large diameter cylindersthrough one of said heads, each of said large pistons being separatelyengageable with said small piston for moving same, and means forsimultaneously directing fluid to said large diameter cylinders forsimultaneously applying force to both said large pistons to impartmovement to said small piston regardless of which large piston is incontact therewith.

27. The actuator of claim 26 in which said small piston has a strokelonger than the stroke of the large pistons and is movable by fluidpressure independently of the movement of the large pistons.

28. The actuator of claim 26 in which the large pistons comprise headsof the small cylinder.

References Cited by the Examiner UNITED STATES PATENTS 645,536 3/00Reardon 91277 1,088,334 2/14 Edgar 92151 2,661,599 12/53 Folmar 92-151RICHARD B. WILKINSON, Primary Examiner.

1. IN A FLUID PRESSURE ACTUATOR THE COMBINATION OF A LARGE CYLINDERHAVING A HEAD AT EACH END THEREOF, A SMALL CYLINDER HAVING AN INNER ANDTELESCOPED IN THE LARGE CYLINDER THROUGH ONE HEAD THEREOF, A LARGEPISTON SECURED ON THE TELESCOPED END OF THE SMALL CYLINDER FOR MOVEMENTIN UNISON THEREWITH AND SLIDABLE IN THE LARGE CYLINDER BETWEEN THE HEADSTEHREON, SAID SMALL CYLINDER ALSO HAVING A HEAD ON ITS OUTER END, ASMALL PISTON SLIDABLE IN THE SMALL CYLINDER, BETWEEN THE HEAD ON THESMALL CYLINDER AND AN ABUTMENT MOVABLE WITH THE LARGE PISTON, ANACTUATOR ROD ATTACHED TO AND MOVEABLE WITH THE SMALL PISTON ANDPROJECTING THROUGH THE OTHER HEAD ON THE LARGE CYLINDER, AND MEANSTHROUGH WHICH PRESSURE FLUID MAY BE DIRECTED INTO AND FROM THE CYLINDERSTO BRING ABOUT RECIPROCATION OF THE PISTONS INDIVIDUALLY AND IN UNISONIN SAID CYLINDERS.